1. Field of the Invention
The present invention relates to a load driving device that performs switching control of an output current flowing through a load.
2. Description of Related Art
FIGS. 22 to 24 are diagrams showing first to third conventional examples of an LED lighting appliance using a light emitting diode (LED) as a light source, respectively. In an LED lighting appliance 200, as a switching control method for controlling an output current ILED flowing through a light emitting diode 201, a so-called peak current control method is adopted. On the other hand, in each of LED lighting appliances 300 and 400, as a switching control method for controlling an output current ILED, a so-called feedback control method is adopted. Each of the LED lighting appliances 200 and 300 is of a non-insulated type (buck type), and the LED lighting appliance 400 is of an insulated type (fly-back type).
One example of prior art related to the above is described in JP-A-2010-110190.
The conventional peak current control method, however, has been problematic in that an input voltage characteristic of the output current ILED is poor, so that the output current ILED fluctuates depending on a variation in an input voltage Vin. Furthermore, the conventional peak current control method has been problematic in that an output voltage characteristic of the output current ILED is also poor, and thus an appropriate peak current should be set in accordance with an output voltage Vout (the number of series stages of a light emitting diode 201) of the LED lighting appliance 200. Moreover, the conventional peak current control method has been problematic also in that the output current ILED varies in accordance with an inductance value of a coil 203.
On the other hand, the conventional feedback control method, though capable of solving the above-described problems, has been problematic in that, compared with the peak current control method, this method requires more complicated and larger circuitry. Particularly in a case of an LED lighting appliance of the insulated type, this method requires that, as a portion used to perform signal transmission from a secondary side to a primary side, a photocoupler 411 whose lifespan is short be provided, and thus has been problematic.